Retaining member with a force threshold



Dec. 17, 1968 J. c. CLASON 3,417,355

RETAINING MEMBER WITH A FORCE THRESHOLD Filed Feb. 10, 1967 llllllll v INVENTOR If C, CZasovz g w wwfm ATTORNEY? United States Patent Office 3,417,355 Patented Dec. 17, 1968 3,417,355 RETAINING MEMBER WITH A FORCE THRESHOLD Jan Christiaan Clason, Hengelo, Netherlands, assignor to N.V. Fabriek Van Electrische Apparaten Voorheen F. Hazemeijer & Co., Hengelo, Netherlands, a corporation of the Netherlands Filed Feb. 10, 1967, Ser. No. 615,176 Claims priority, application Netherlands, Feb. 15, 1966, 6601931 4 Claims. (Cl. 335-296) ABSTRACT OF THE DISCLOSURE A retaining member with a force threshold applicable to an electric switch and comprising stub and cup-shaped members relatively movable with retaining elements and surrounded by spring and magnetic action.

This invention is applicable to an apparatus as disclosed in application Ser. No. 427,007 filed Ian. 21, 1965, now Patent No. 3,331,930.

This invention relates to a retaining member with a force threshold, comprising a stub and a cup-shaped member which are capable of moving relative to each other, the said stub being positioned in the coupled position of the retaining member, in the cup-shaped member and being provided with a circular groove in its annular surface, into which groove one or more retaining elements are forced by spring action, through recesses in the wall of the cup-shaped member.

"In the known device, which in this case is applied to an electric switch, the stub and the cup-shaped member are attached to relatively movable switch portions, respectively, while round the cup-shaped member are provided two parallel rods coupled at the ends by tension springs, the middle of said rods being positioned in the interior of said cup, through recesses in the cup wall. In the engaged position of the switch the stub is positioned in the cup in such a way that the rods rest in the groove of the stub.

When a switch equipped with a known device is to be disengaged, first such an amount of mechanical energy must be accumulated that the rods are forced out of the groove of the stub, after which the switch is disengaged with a given initial velocity. The value of this force threshold to be overcome depends exclusively upon the tension in the tension springs of the rods, the cross-section of the groove, and the shape of the retaining elements.

In case of a short circuit the movable switch portion is subjected to electrodynamic forces, which tend to drive said portion in the direction of disengagement. If in consequence the fixed force threshold is exceeded, the switch is disengaged, which is undesirable. The choice of a higher force threshold entails a heavier disengagement mechanism, which is not attractive or advisable.

The object of the present invention is a retaining device, in particular for an electric switch, the force threshold of which is adjusted at a higher value by external magnetic fields, and to this end provides a device of the type mentioned, which is characterized in that roundthe cupshaped member there is provided a magnetic circuit closed in itself, comprising several elements of magnetizable material placed one behind the other in a cyclic sequence, movable at right angles to the circumferential direction of the magnetic circuit, and resting against the retaining elements, between which magnetizable elements narrow air gaps are provided, a source of external magnetic fields being provided with a view to the magnetic energization of the magnetic circuit.

It is therefore a further object of the invention to provide elements of magnetizable material preferably having the form of levers shaped like sectors of a ring, which levers near their pivotally supported ends rest against the retaining elements, the component parts of the magnetic circuit being surrounded by an annular spring.

In the device according to the invention for an electric switch the magnetizable elements of the magnetic circuit are magnetized by the magnetic fields, which are produced by the short circuit current, in consequence of which the magnetizable elements are subjected to inwardly directed magnetic forces, which are transmitted to the retaining elements. The total force with which the retaining elements are forced .into the groove on the stub has thus been increased, so that the force threshold to be overcome if the switch is to be disengaged, has been heightened.

The invention Will now be explained more fully by reference to the annexed drawing, which represents an embodiment of the device according to the invention and in which FIG. 1 is a longitudinal section of the device on the line II in FIG. 2 in the direction of the arrows, and

FIG. 2 is a cross-section taken on the line IIII in FIG. 1 in the direction of the arrows.

As shown on the drawing, the retaining member according to the invention comprises a stub member 1 provided with a buffer element 3, which stub member in the coupled position of said retaining member, as shown in the drawing, is positioned in the cup-shaped member 4. The stub member 1 is provided with a groove 2, into which the retaining elements 6 are forced, through recesses 5 in the cup wall, by the annular spring 7 by means of the magnetizable elements 8. The spring 7 is held in fixed position by means of the grooves 11 in the exterior surface of the magnetizable elements 8. For the disengagement of the retaining member the stub 1 must be pulled upwards in FIG. 1, whereby the retaining elements 6 are then forced outwards by the lower inclined edge of the groove 2. In consequence, the magnetizable elements 8 pivot slightly outwards about their pivots 10, as a result of which the annular spring 7 is extended. The longitudinal recesses 12 in the cup wall permit the pivoting movement of the magnetizable elements 8. In the absence of magnetic fields the magnetic circuit, formed by the magnetizable elements 8 and the air gaps 9, is not energized and the pulling force or force threshold is a constant quantity.

When, however, the magnetic circuit is energized, in the air gaps 9, magnetic fields will flow, which counteract the outward pivoting of the elements 8 and thus cause a heightening of the holding force.

The energization of the magnetic circuit 8 and 9 may be effected in various ways.

When, however, the device according to the invention is applied to an electric switch, in case of a short circuit, it is automatically energized by the strong magnetic fields produced by live conductors R, R; S, S; T, T; FIG. 2.

I claim:

1. A retaining member with a force threshold, comprising a cup-shaped member having at least one recess in a wall thereof, a stub member in the cup-shaped member with both members capable of moving relative to each other, the said stub member having a circular groove in its annular surface and being positioned in the coupled position of the retaining member, in the cup-shaped member, a retaining element in the recess in the wall of the cup-shaped member, a closed magnetic circuit around the cup-shaped member comprising a plurality of elements of magnetizable material placed one behind the other in a circle around the cup-shaped member and movableat right angles to the circumferential direction of the magnetic circuit and resting against the retaining element, said elements of magnetizable material having narrow air gaps between them, a spring around the elements of magnetizable material to urge them inwardly, and a source of external magnetic fields provided for the magnetic energization of the magnetic circuit.

2. A retaining member according to claim 1, in which the elements of magnetizable material have the form of levers in the shape of sectors of a ring, said levers near their pivotally supported ends resting against the retaining element.

3. A retaining member according to claim 1, in which the wall has a plurality of recesses and a retaining element is provided in each recess, the retaining elements being in the form of balls.

4. A retaining member according to claim 1, in which the stub member is provided with an end rim to contact the retaining element.

References Cited UNITED STATES PATENTS 2,775,137 12/1956 Chung 74-527 XR 3,293,382 12/1966 Lewandowski et a1. 74527 XR 10 GEORGE HARRIS, Primary Examiner.

U.S. Cl. X.R. 74527 

